This invention relates to an apparatus for performing mammography and/or tomosynthesis (in particular, digital breast tomosynthesis) and equipped with a device for removing diffuse radiation.
Known in the prior art are apparatuses designed to perform both digital breast tomosynthesis (DBT) and mammography.
These apparatuses comprise an X-ray source and a detector configured to receive the X-rays emitted by the source.
It should be noted that the patient's breast being analyzed is interposed between the X-ray source and the detector in such a way that the X-rays emitted by the source pass through the breast
Generally speaking, the breast is placed on a suitable rest and compressed by a plate known as compressor.
As is known, in the breast being analyzed X-rays are absorbed to a different extent by parts affected by tumor growths or the like as compared to parts without tumor growths. A radiographic image obtained from the X-rays received by the detector can thus be analyzed to identify suspected tumors.
When X-rays pass through a part of the human body such as the breast, however, secondary photons are generated. These secondary photons (also known as “scattering radiation” or “diffuse radiation” or “secondary radiation”) propagate in different directions relative to the rays emitted by the X-ray source (that is, relative to the radiation referred to as “primary” radiation).
This secondary radiation, if it is not adequately intercepted and attenuated, strikes the detector device together with the primary radiation and is detected by the detector device. As a result, the quality of the radiographic image obtained is appreciably poorer (loss of sharpness and contrast) on account of the noise produced by the secondary radiation.
To improve the quality of the radiographic images, these apparatuses are equipped with a system which is interposed between the breast and the detector device and which removes the diffuse radiation by collimation of the primary radiation.
An implementation typical of mammography is accomplished by a grille of plates which, in use, are arranged substantially at a right angle to the patient's chest, that is to say, in such a way that the planes defined by the large planar faces of the plates is almost at a right angle to the plane defined by the patient's chest.
This grille allows the secondary radiation incident upon the detector device to be reduced and thus improves the inherent contrast and spatial resolution of the mammographic images.
Where the X-rays are emitted from a plurality of different positions relative to the detector device, as in the case of tomosynthesis where the sources are movable relative to the detector, collimation of the primary beam would require a different orientation of the plates for each position. Vice versa, the use of a typical mammographic grille for all the tomosynthesis projections would produce the negative effect of attenuating the primary beam for each position different from the position for mammography. It should be noted that poor image quality is particularly evident at the limit positions adopted by the X-ray source relative to the detector.
To date, this problem is avoided by removing the grille when the apparatus is used for tomosynthesis.
Removal of the grille may be automated or manual.
It should be noted that if the grille has to be removed manually by the operator, the breast must be decompressed (that is, the patient must be made to move) to allow the grille to be removed. In this case, therefore, it is not possible to perform both mammography and tomosynthesis in combination while compressing the breast only once, which means that spatial adjustment of the images is more difficult and that it is impossible to save an X-ray dose as a result of using mammography as one of the projections for the tomosynthesis examination. Moreover, manual removal of the grille is awkward for the operator and for the patient. The grille must be handled with great care (to avoid damage caused if it is dropped or knocked against a hard surface).
Automated grille removal during a combined examination, on the other hand, takes some time and involves discomfort for the patient, whose breast remains compressed while waiting for the automatic system to remove the grille. Moreover, the overall dimensions of the apparatus are appreciably increased on account of the need to provide a zone where the grille can be housed when it is not operatively interposed between the breast and the detector.
A need which is strongly felt by operators in this field is that for an apparatus which can provide good quality mammographic/tomosynthesis images (that is, sharp images with a good quality contrast) during both tomosynthesis and mammography without having to remove the grille.